What is an Autotransformer Explained

By R.W. Hurst, Editor

What is an Autotransformer?

What is an Autotransformer?

An autotransformer is an electrical transformer with only one winding that acts as both the primary and secondary winding. Unlike traditional transformers with separate windings, an autotransformer uses a single coil acting as both the input and output, depending on the tapped point. This single winding structure allows for significant material savings, notably the savings of copper in an autotransformer, which can lead to cost reductions and improved efficiency.

Basic Principle and Construction

The basic principle relies on a single winding with a tap that divides the coil into two parts: the primary winding and the secondary winding. The primary and secondary circuits are common to both the primary and secondary windings, meaning they share a portion of the winding. This construction enables it to adjust the voltage level by varying the position of the tap.

In a typical autotransformer, the primary winding is connected to the supply voltage, while the secondary voltage is taken from the tap point. The output voltage is proportional to the turns ratio between the tapped sections of the winding. This arrangement allows it to efficiently step up or step down the voltage as required.

Advantages and Disadvantages

Autotransformers offer several advantages:

Efficiency: Due to the shared winding, autotransformers exhibit lower losses and higher efficiency compared to conventional transformers with separate windings.
Cost-Effectiveness: The reduced use of materials, especially copper, results in lower manufacturing costs.
Compact Size: The single winding design makes it more compact and lighter.

However, there are also disadvantages:

Lack of Isolation: Since the primary and secondary sides are electrically connected, there is no isolation between them, which can be a safety concern.
Short Circuit Risk: If the common winding gets short circuited, it can lead to severe damage.
Limited Voltage Range: Autotransformers are less suitable for applications requiring significant voltage differences between the primary and secondary sides.

Applications

They are used in a variety of applications where the voltage adjustment does not require electrical isolation:

Voltage Regulation: They serve as voltage regulators in power distribution systems to maintain a stable voltage level.
Motor Starting: They provide reduced voltage to start motors, reducing inrush current and preventing electrical stress.
Variable Voltage Supply: In laboratory settings, they provide adjustable output voltage for testing purposes.
Power Transmission: They are used in power transmission to step up or step down voltages efficiently.

Differences Between Them and Two-Winding Transformers

The primary difference lies in their construction and operation. In an autotransformer, the primary and secondary windings are a single coil acting as both, whereas a two-winding transformer has separate windings for each. This fundamental difference impacts several aspects:

Material Usage: Autotransformers use less copper and iron, leading to lower costs.
Efficiency: With fewer windings and less resistance, they are more efficient.
Isolation: Two-winding transformers provide electrical isolation between the primary and secondary circuits, which is not possible in autotransformers.

Safety Considerations

When using an autotransformer, safety is paramount due to the lack of isolation between the primary and secondary sides. Here are key considerations:

Proper Grounding: Ensure the transformer is correctly grounded to prevent electrical shock hazards.
Overload Protection: Implement protective devices to guard against overloads and short circuits, which can cause severe damage due to the shared winding.
Voltage Drop Monitoring: Regularly monitor the voltage drop across the autotransformer to detect potential faults or inefficiencies.
Inspection and Maintenance: Regular inspections and maintenance are crucial to ensure the device operates safely and efficiently.

What Is An Autotransformer? It is valuable in applications requiring efficient voltage regulation and transformation without the need for electrical isolation. Understanding their construction, benefits, limitations, and safety considerations is essential for their effective and safe use.

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Evluma Launches Line of Post Top Globes to Complement LED OmniMax

March 12, 2020, Renton, WA…Street and area lighting manufacturer Evluma, announces the release of a new globe accessory line, OmniMax Lighting Solutions (OLS) to complement their OmniMax family of LED replacement lamps. OLS is a custom, curated selection of spherical and acorn style globes for decorative streetlights. The OmniMax is a Bluetooth-connected, screw-in replacement lamp for use in decorative post top globe and acorn lights. The release of a globe line to complement the OmniMax is designed to make the HID to LED conversion and maintenance process easier for Evluma customers.

Customers executing a retrofit project can conveniently purchase a replacement globe at the same time they purchase the OmniMax. “The wide variety of styles and materials offered means that we can typically provide a customer with a globe that matches an older style,” said Marketing Director, Cathleen Shattuck. “Customers can refresh globes simultaneously with OmniMax installation to save on labor, or if they suddenly discover damage to individual light fixtures, we can quickly provide them with a solution. Our high level of customer service means we are well-adapted to quick turnaround on orders of any size, keeping the process convenient and low cost.”

Using OmniMax, municipalities, utilities and electric departments converting post top fixtures from HID to LED can do so in under 5 minutes a fixture. The OmniMax is available in both Premium and Standard models. Premium models are Bluetooth-enabled and are compatible with Evluma’s wireless control application, ConnectLED. Both models carry a ten-year warranty and offer Evluma’s signature low-glare illumination.

About Evluma

Formed in 2008, Evluma is committed to developing affordable, long-lasting and environmentally low-impact LED lighting solutions that fundamentally change the landscape of the outdoor utility lighting market. Evluma’s high standard of customer service and background in innovative lighting technologies, automation and software design creatively ideate and inform its utility-grade products. Evluma is located in Renton, WA, USA.

09/24/20

Evluma's Build-Your-Own Acorn is an Affordable Answer to Decorative Streetlight LED Upgrades

Street and area light manufacturer Evluma announces the release of Build-Your-Own Acorn; a full-fixture, decorative streetlight replacement solution that includes the customer’s choice of acorn globe, finial and capital fitter. This solution is designed for utilities, municipalities, facilities and property managers looking to upgrade their existing decorative lighting from HID to LED and features the OmniMax™ LED lamp as its light source.

“Build-Your-Own-Acorn is a tailored solution that puts control in the hands of the customer,” said Evluma Product Manager Jason Dobbs. “With the value-driven OmniMax at the center of quality, cost-effective options, this is an affordable approach to complete head replacements. Build-Your-Own-Acorn offers the freedom to replace and repair fixtures without being locked into a proprietary OEM solution that may be hard to change later and typically costs more. It’s everything but the pole.”

Build-Your-Own Acorn includes multiple styles of acrylic and polycarbonate globes, in addition to a cast aluminum capital fitter. The capital fits 3 inch and 4 inch poles and is offered in black or green. The 70W OmniMax LED lamp is offered in six different color temperatures ranging from 2000K-5000K in either the Premium or Standard. OmniMax Premium includes Evluma’s patented, maintenance-saving Photocontrol Failsafe™ and compatibility with Evluma’s Bluetooth lighting app ConnectLED™. OmniMax Standard ships without connectivity features or Photocontrol Failsafe built-in.

“Photocontrol Failsafe means never having to replace a failed photocontrol ever again,” said Janine Soper, Evluma’s Regional Sales Manager. “With ConnectLED, the OmniMax Premium can be quickly dimmed or programmed with a dimming schedule, offering additional aesthetic and energy saving opportunities,” said Janine.

Both OmniMax models are supported by robust 20kV/10kA surge protection and the OmniMax’s four layers of thermal management for extended operation in enclosed environments. The capital has a 5 year warranty on the finish. Acrylic globes are warrantied for 5 years against yellowing. The OmniMax and all electronics, including the capital’s optional photocontrol are warrantied for 10 years.

About Evluma

02/22/21

Parallel Resonant AC Test Sets

High Voltage, Inc. is an American test equipment manufacturing company located in rural Copake, NY. We are known for high quality, easy to use equipment and for our commitment to providing the best customer and product support in the industry.

As we matured we expanded into larger products. Cable fault locators (thumpers) as well as higher power ac (HPA) dielectric testers as might be used in a factory environment. Our HPA line of ac testers are available with outputs up to 300 kV ac and power levels up to 40 kVA and can be customized with various levels of control sophistication.

Our new PAR line of ac dielectric testers are designed to meet the needs of those who need power levels up to 250 kVA, to be able to test their highly capacitive test loads. Using ac resonant technology outputs of 50 kV at 5A (for example) are possible with an input of only 230 v, 90 A. That is an input of 20 kVA for an output of 250 kVA. (Model PAR-50250FC5)

The PAR models consist of a control section and a high voltage section. While large, they are transportable by van or trailer for field work. The control section includes the input breaker, variable (motorized) input control, a PLC controller, and connections for controlling the hv section. The high voltage section is a steel tank with a phenolic output bushing. Inside this tank is a variable-core reactor in an insulating oil bath with an air space at the top to allow for thermal expansion.

The variable reactor looks similar to a transformer but has a moveable core that allows the inductance value to vary to match the capacitance of the load, thereby achieving resonance. This effectively cancels the load capacitance, as far as input power requirements are concerned. Once in resonance, the input voltage is increased until the desired output voltage level is achieved. For a capacitive load that must be tested at power frequency the PAR reduces power requirements, as well as test equipment size by one tenth to one thirtieth, compared to a test transformer.

The HVI PAR family of resonant as dielectric testers are perfect for power frequency testing of power cables, rotating machinery, bushings, instrument transformers, transformers, shunt reactors, and many other products.

For more info please contact sales@hvinc.com to discuss your application.
For more information on these and other high voltage test products, contact High Voltage, Inc. at www.hvinc.com, sales@hvinc.com, or call 518-329-3275.

03/07/22

Evluma Launches Low-Glare LED Roadway Luminaire

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This sleek and stylish luminaire was designed with RP-8-18 roadway requirements in mind. The unique optical design offers a combination of roadway performance and glare control unprecedented in the industry. “RoadMax is an advancement of Evluma’s reputation for low-glare, visually-pleasing outdoor lighting,” says Taisha Bezzo, National Sales Director. “RoadMax addresses contemporary concerns regarding disability glare and light trespass from roadway lighting while maintaining exceptional pole spacing.”

Multiple luminaire configurations for Type II, Type III and Type V, all with zero-uplight (U0), are offered. Additional features such as a field adjustable wattage selector (FAO), light trespass shields and a choice of photocontrol sockets are available. RoadMax can be customized to include Evluma’s Photocontrol FailsafeTM, a patented technology that solves photocontrol failures on street and area lights. Compatibility with ConnectLEDTM, Evluma’s Bluetooth app for wireless lighting controls, enables dimming and dimming schedules without the need for a network. Evluma’s comprehensive 10-year warranty and signature 20kV/10kA surge protection comes standard with every model.